One of the things that I love about the iPad's on-screen keyboard is the way that you can hold your finger on certain keys to bring up a menu of related keys: "a" gives you "a", "à", "á", "â", "ä", "ā", "å", "ã", and "æ"; "$" gives you "$", "¥", "€", "¢", "£", and "₩"; and so on. I'd like to extend this behavior to provide access to some characters that were overlooked: for instance, I do a fair amount of footnoting, and would love to set up the single- and double-headed daggers that are often used in footnotes as alternative characters for the "*" key. Are there any keyboard tweaks out there that do this sort of thing, and/or how would I go about writing a tweak that does this sort of thing?